The invention relates to a process for drawing off deformable masses containing air, especially for drawing off sausage, in which the mass is transferred in a stream from a supply space into a filling cylinder where a vacuum is applied to remove air from the mass, and in which the transferred mass is then ejected from the filling cylinder by means of a piston arranged in the cylinder.
The invention also relates to an apparatus for carrying out such a process, having a filling funnel with a filling cylinder connected to the filling funnel via an orifice closable by means of an inlet slide. A piston is arranged in the filling cylinder which has a slide-controlled outlet orifice through which the mass conveyed from the filling funnel into the filling cylinder can be ejected in meterable quantities by controlling the piston stroke. Further means are provided for placing the filling cylinder under vacuum when it is filled with mass from the filling funnel.
A process and apparatus of this type is known from European Patent published Application No. 129,703. There, the mass to be drawn off is first introduced into a filling funnel. After the filling funnel has been closed with a cover, a vacuum is generated in the filling funnel. The introduced mass is stirred by an agitator to ensure that air bubbles included in the mass escape. The filling funnel is separated from the filling cylinder by an inlet slide at the bottom of the filling funnel.
To prepare the filling cylinder for filling with the mass located in the filling funnel, the piston of the filling cylinder is moved downwards to generate a vacuum in the cylinder. The pressure than obtained in the filling cylinder is at least maintained by a vacuum pump connected to the cylinder. The inlet slide is then opened, and the mass in the filling funnel is sucked into the filling cylinder as a result of the pressure difference between the filling funnel and the filling cylinder. As it passes through the inlet slide into the filling cylinder, the mass separates as a result of the pressure difference obtained and the high transfer speed. As a result, any residual air bubbles included in it escape from the mass and are sucked off by the vacuum pump. Filling of the cylinder takes place until the filling cylinder is completely filled up and then the inlet slide is closed. Subsequently, a slide in an outlet orifice of the filling cylinder is opened, and the mass to be drawn off, now located in the filling cylinder, is ejected through the outlet orifice by controlling the piston stroke, in order, for example, to fill a tube of sausage skin or cans.
However, this known process and the apparatus described have some disadvantages.
Although it is possible, because of the pressure difference generated between the filling funnel and the filling cylinder, to transfer the mass to be drawn off from the filling funnel into the filling cylinder at a relatively high speed, this being advantageous to achieve a high filling capacity, nevertheless this does not guarantee that air will be removed to a sufficient extent from the air-containing mass. This is because the volume maintained under vacuum in the filling cylinder changes continuously during the filling operation as the level of the introduced mass increases gradually from the cylinder bottom until the filling cylinder is full. Thus the free cylinder volume will gradually decrease. However, it is impossible to maintain a constant and uniform vacuum in a constantly changing volume, so that differing conditions arise on the surface of the mass depending on the filling level, and hence a uniform evacuation of air from the inflowing mass is not possible.
An even more serious disadvantage is that, when the slide is opened, the mass to be drawn off falls from the funnel into the filling cylinder particularly in the direction of the main axis of the cylinder. The mass stream, when it enters, at the same time brings air with it into the mass already present in the filling cylinder. The mass stream falling in sinks relatively deep into the mass already present, thus producing relatively deep air inclusions inside the mass which can no longer be eliminated by the vacuum in the remaining volume of the cylinder not yet filled up.
The higher the inflow speed and the more fluid the mass is to be drawn off, the more serious these problems become.
A further disadvantage is that a vacuum has to be generated in the filling funnel itself, in order to obtain a sufficient evacuation of air from the mass to be drawn off. A particular disadvantage of this, beside the equipment and lines additionally required for the purpose, is that the filling funnel cannot be filled at any time desired, because to do this the funnel first has to be aerated and the cover then has to be removed. After filling, the necessary vacuum then has to be generated once again before transfer of the mass to the filling cylinder.
Finally, a further disadvantage is that the filling speed cannot be controlled accurately. In principle, although the drawing-off speed can be influenced by preselecting a specific pressure difference between the filling funnel and the filling cylinder, it is nevertheless impossible to have an accurate control because the filling speed is also dependent on other variables, especially the consistency of the particular mass to be drawn off. Since the filling speed is controlled by means of the pressure difference, fluctuations in the differential pressure can be recognized directly by corresponding fluctuations in the filling speed. On the other hand, since the filling speed acts in turn on the degree of evacuation of the sausage mass, fluctuations in the differential pressure likewise prevent a uniform removal of air from the mass to be drawn off.